1. Field of the Invention
The present invention relates to a data driver for a liquid crystal display device, comprising voltage buffer amplifiers each outputting an analog gradation voltage, applying the analog gradation voltages to data bus lines such that voltage polarities of adjacent data bus lines concerned with a same display color are inverse to each other, and more particularly, to a data driver for driving the data bus lines of a liquid crystal display device in a dot inversion fashion regarding time and space.
2. Description of the Related Art
FIG. 8 shows the output stage of a prior art data driver 10X connected to the data bus lines of a liquid crystal display (LCD) panel.
The voltage buffer amplifiers B1 to B12 of the data driver 10X are respective voltage followers, and the outputs thereof are connected to the respective data bus lines D1 to D12 of the LCD panel. The data driver 10X drives the data bus lines in a dot inversion fashion regarding time and space. That is, voltages applied to adjacent data bus lines at the same time have inverse polarities to each other, and analog gradation voltages corresponding to display data are outputted from the respective voltage buffer amplifiers B1 to B12 such that voltage polarity of each data bus line is inverted every horizontal period. According to the dot-inversion driving technique, potential variations of a pixel electrode caused by cross capacitance between a data bus line and a scan bus line can be effectively canceled and further, a common potential of the opposite electrode can be stabilized, resulting in reducing a flicker.
However, charge and discharge currents of each of the voltage buffer amplifiers B1 to B12 are relatively large, leading to higher power consumption.
Facing such a disadvantage, in order to effectively utilize electric charge accumulated on the data bus lines and decrease power consumption, short-circuiting switches S1 to S12 are connected between a common line CL and the respective data bus lines D1 to D12. When the outputs of the voltage buffer amplifiers B1 to B12 are rendered to be in a high impedance state during a horizontal blanking period, the short-circuiting switches S1 to S12 are simultaneously turned on. Thereby, potentials of the data bus lines D1 to D12 are rendered to be nearly equal to the common potential of the opposite plane electrode of the liquid crystal display panel, enabling a current to be consumed in the voltage buffer amplifiers B1 to B12 to reduce up to a half.
However, since a necessity arises that the short-circuiting switches are provided to the respective voltage buffer amplifiers, an occupied area of the data driver 10X increases, thereby disturbing higher density of data bus lines in arrangement.
FIG. 9 shows a data driver 10Y of a dot inversion driving type disclosed in JP 10-282940 A.
In this circuit, short-circuiting switches S1 to S9 are connected between every other adjacent data bus lines. With this circuit, since the number of the short-circuiting switches is reduced to a half that of FIG. 8, the above described problem can be solved.
However, since different color signals are provided onto adjacent bus lines, there is no correlation therebetween and an efficiency of utilization of electric charge accumulated on the data bus lines is not so satisfactory. For example, potentials of the data bus lines D1 to D6 are distributed in a horizontal period as shown in FIG. 10, and when the short-circuiting switches S1, S3 and S5 turns on in the next horizontal blanking period, the potentials are distributed as shown in FIG. 11 to produce differences between each potential of the data bus lines and the common potential VCOM of the opposite electrode, which increases power consumption of the data driver 10Y compared with the case of FIG. 8. Further, the differences become a cause for variations in the common potential VCOM, resulting in generation of a flicker.
Accordingly, it is an object of the present invention to provide a data driver for a liquid crystal display device, capable of not only suppressing increase in circuit area but also reducing power consumption together with alleviating a flicker.
In a first aspect of a data driver for a liquid crystal display device according to the present invention, short-circuiting switches are intermittently connected between adjacent data bus lines concerned with a same display color, and the short-circuiting switches are turned on when the outputs of the voltage buffer amplifiers or locations between the voltage buffer amplifiers and the respective data bus lines are in a high impedance state.
Pixel data signals in the adjacent same color have inverse polarities, and it is a high probability that absolute values thereof are nearly equal. Particularly, this probability is higher in a region of a background image. Hence, with this data driver for a liquid crystal display device, by turning on the short-circuiting switches, the potentials of the data bus lines become nearly equal to a common potential of the opposite electrode of a LCD panel, whereby a current to be consumed in the voltage buffer amplifiers can be reduced more than in a case where short-circuiting switches are intermittently connected between adjacent data bus lines.
Further, since the common potential is stabilized, a flicker is alleviated, and thereby an image quality is improved compared with a case where short-circuiting switches are intermittently connected between adjacent data bus lines.
In addition, since the number of the short-circuiting switches is smaller than a case where a short-circuiting switch is connected between each adjacent data bus lines, the circuit area of the data driver can be reduced.
In a second aspect of a data driver for a liquid crystal display device according to the present invention, the short-circuiting switches are connected through interconnecting lines arranged in first and second rows in a staggered configuration in the above described first aspect.
With this data driver for a liquid crystal display device, since the short-circuiting switches and the interconnecting lines for them are arranged such that the densities thereof are nearly uniform, the circuit area of the data driver can be narrower, and the higher density of the data bus lines can be realized.
In a third aspect of a data driver for a liquid crystal display device according to the present invention, the short-circuiting switches are formed at one side of every other data bus lines in the above described second aspect.
With this configuration, the above-described effect is further enhanced.
Other aspects, objects, and the advantages of the present invention will become apparent from the following detailed description taken in connection with the accompanying drawings.